This document discusses Giardia lamblia, a unicellular parasite that causes giardiasis. Some key points:
- G. lamblia was first observed by Van Leeuwenhoek in 1681 and causes traveler's diarrhea or beaver fever. It inhabits the small intestine as a trophozoite attached to the mucosa.
- The infective stage is the cyst, which is ingested through contaminated food or water or from contact with infected flies or food handlers. The cyst contains 4 nuclei and can survive outside the host.
- Symptoms of giardiasis include diarrhea, flatulence, and greasy stool. The infection is common in children. The
LUMEN DWELLING FLAGELLATES - GIARDIA
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INTERNATIONALLY ACCEPTED BOOK OF MEDICAL PARASITOLOGY BY K. D. CHATTERJEE
TEXT BOOK OF MEDICAL PARASITOLOGY BY PANIKER
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Entamoeba histolytica was first discovered by Losch in 1875.
It is worldwide distribution.
It is prevalent in tropical and subtropical countries where sanitary conditions are poor.
In india, it is prevalent in Chandigarh, Tamil Nadu & Maharashtra.
It is found in the colon of man.
It is monogenetic because the whole life cycle completed within a single host, i.e. man.
LUMEN DWELLING FLAGELLATES - GIARDIA
REFS:
INTERNATIONALLY ACCEPTED BOOK OF MEDICAL PARASITOLOGY BY K. D. CHATTERJEE
TEXT BOOK OF MEDICAL PARASITOLOGY BY PANIKER
IMAGE SOURCES : FROM INTERNET
Entamoeba histolytica was first discovered by Losch in 1875.
It is worldwide distribution.
It is prevalent in tropical and subtropical countries where sanitary conditions are poor.
In india, it is prevalent in Chandigarh, Tamil Nadu & Maharashtra.
It is found in the colon of man.
It is monogenetic because the whole life cycle completed within a single host, i.e. man.
Giardia lamblia is also known as Lamblia intestinalis and Giardia duodenalis
It is a flagellated parasite that colonizes and reproduces in the small intestine, causing giardiasis.
Esta parasitosis producida por Giardia intestinalis (G. duodenalis o G. lamblia) es predominante en niños y presenta en la actualidad una prevalencia creciente tanto en países tropicales como no tropicales
Giardia lamblia is also known as Lamblia intestinalis and Giardia duodenalis
It is a flagellated parasite that colonizes and reproduces in the small intestine, causing giardiasis.
Esta parasitosis producida por Giardia intestinalis (G. duodenalis o G. lamblia) es predominante en niños y presenta en la actualidad una prevalencia creciente tanto en países tropicales como no tropicales
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It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
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What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
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2. Giardia lamblia
• traveler diarrhea or beaver fever
• unicellular parasite
• Initially found by Van Leeuwenhoek in 1681
• named after Alfred Mathieu Giard (Clinical
Microbiology Review, 2001).
4. Giardia lamblia
Causes : Giardiasis in man especially children.
Geological Distribution: Cosmopolitan.
Habitat : Duodenum, upper part of small intestine, bile ducts and gall
bladder as trophozoites attached to the mucosa.
D.H: man R.H: animals
Infective stage : the cyst.
Mode of infection:
Contaminated food or water
Flies and food handlers
Faeco-oral Trophozoite
Cyst
5.
6. Giardia lamblia
Morphology of Cyst stage:
Average size 12 X 7 µ
Oval with well defined cyst wall
Four nuclei present usually at one pole.
Includes: axostyle – parabasal bodies – remnants
of flagella
7. Giardia lamblia
Morphology of Trophozoite stage:
Average size 15 X 8 µ
Pear shaped (broad anteriorly –tapering posteriorly)
Convex dorsally –flat ventrally with bilobed anterior
concavity (sucking discs) for attachment.
Motility by 4 pairs of flagellae (similar to a falling leaf)
Two oval nuclei with central karyosome.
Two axostyle traversing the body
Two rod-shaped parabasal bodies across the
axostyle
11. • Giardia infected patients complain of
diarrhoea and flatulence.
• Stool of Giardia infected patients is light-
coloured and greasy.
• G. lamblia infection is common in children.
• Giardia cysts are infective to man.
12. Muller, J., G. Ruhle, N. Muller, JF. Rossignol and A. Hemphill.
2006.In Vitro Effects of Thiazolides on Giardia lamblia
WB Clone C6 Cultured Axenically and in Coculture with
Caco2 Cells. American Society for Microbiology.50:1
(162–170).
Mohamed, R. 2003. Giardia lamblia.
Editor's Notes
Giardia lamblia, also known as traveler diarrhea, or beaver fever, is a unicellular parasite that is found in the fecal matter of infected mammals. Initially found by Van Leeuwenhoek in 1681 after studying his own fecal matter, Giardia lamblia was named after Alfred Mathieu Giard because of his lasting research on the parasite (Clinical Microbiology Review 2001).
Protista- All members of this kingdom are eukaryotic and contain most commonly unicellular organisms
Sarcomastigophora- are categorized as being flagellated, and are usually 10-20 micrometers in size. (Contain either free-living or parasitic protozoan. )
Zoomastigophora- how organisms move through the use of one or more flagella.
Diplomondida- contains mostly parasitic organisms. These organisms don’t possess a mitochondria or Golgi apparatus, but instead contain mitosomes, which involve the growth of iron sulfur proteins.
Hexamitidae - having six or eight flagella, these organisms contain two true nuclei, also bilaterally symmetrical.
Giardia- The genus Giardia contains anaerobic parasites that feed off of and reproduce in the small intestine of humans and other mammals. These organisms have two stages of life, one in which it is a swimming trophozoite and the other in which it is a cyst feeding off the host organism. Giardia lamblia- most commonly associated with the disease giardiasis, can be distinguished from other Giardia species because of the two vertical adhesion disks on the top of the organism. These disks allow the organisms to attatch to the hosts small intestine and retain nutrients from the host. The name Giardia lamblia literally means flagellated protozoan.
